cc @stamblerre

Errors are associated with positions in a file, and if there's no position, the error is printed with a -. See the documentation of error here. https://pkg.go.dev/golang.org/x/tools/go/packages?tab=doc#Error

The error's already associated with a package, so the error doesn't print its own package to avoid redundancy.

Can we make "go build" follow the same convention then? I.e., make it print "-:" instead of "package nonexist:"?

@jayconrod @bcmills

I don't know if that's the right thing to do here: the closer analogue to what go packages does is go list -e -json: and with those you get a very similar result:

$ go list -e -json nonexist
{
	"ImportPath": "nonexist",
	"Match": [
		"nonexist"
	],
	"Incomplete": true,
	"Error": {
		"ImportStack": [
			"nonexist"
		],
		"Pos": "",
		"Err": "package nonexist is not in GOROOT (/usr/local/go/src/nonexist)"
	}
}

Looks like cmd/go's "package nonexist:" output comes from:

I don't think -: is a particularly helpful prefix. (Helpful to tools, perhaps, but confusing to humans.)

That said, package nonexist: cannot find package "nonexist" is unpleasantly redundant too. This failure message is a lot smoother in module mode than in GOPATH mode:

example.com$ GO111MODULE=on go build nonexist
package nonexist is not in GOROOT (/usr/local/google/home/bcmills/sdk/gotip/src/nonexist)

example.com$ GO111MODULE=off go build nonexist
package nonexist: cannot find package "nonexist" in any of:
        /usr/local/google/home/bcmills/sdk/gotip/src/nonexist (from $GOROOT)
        /tmp/tmp.00bJBNCJEL/_gopath/src/nonexist (from $GOPATH)

If someone wants to fix the GOPATH-mode error message to match the module-mode one, that seems like it would be an improvement, but unless we see something similar in module mode I don't think it's worth spending much time on.

On the go/packages side, one thing we can do is just drop the "-:" on the error's String method. That might be nicer for users if the package?